Crown restorations providing aesthetics similar to natural teeth include metal ceramic dental restorations and all ceramic dental restorations, both of which are formed with dental porcelain. When these dental restorations are formed, techniques are used for expressing white bands, and stains around cervical portions and proximal surfaces, hair lines, enamel cracks and the like on natural teeth to mimic natural teeth. For this, color-adapting compositions used in ceramic crown porcelain (hereinafter sometimes referred to as “porcelain stain”) is used.
Porcelain stains comprise matrix glass and inorganic pigments for coloring.
Generally, techniques for coloring crown restorations to mimic natural teeth include an internal stain technique in which a porcelain stain is used between porcelain portions and an external stain technique in which a porcelain stain is used on the outermost surface of a porcelain portion.
In addition, some of all ceramic crown restorations are formed with various materials such as castable ceramics for a casting process, pressable ceramics for a heat pressing process, CAD/CAM blocks applicable for a CAD/CAM system and the like, and the aesthetic is enhanced by applying a porcelain stain on the surfaces of those crown restorations
Usage of porcelain stains is explained below. Firstly, a porcelain stain having an appropriately selected color is placed on a glass plate or a stain palette. Porcelain stains are provided in a form of paste or powder. Therefore, when a porcelain stain is in a form of paste, an appropriate amount of the paste itself is placed on a glass plate or a stain palette, and when a porcelain stain is a form of powder, an appropriate amount of powder is placed on a glass plate or a stain palette and, then, an exclusive liquid is added to knead them into a paste form.
Desired colors may be obtained by blending porcelain stains having different colors at arbitrary ratios. When it is desired to modify application properties or kneading properties for those kneaded to blend colors, a thinning liquid may be appropriately added and kneaded.
The color adapted porcelain stain paste is applied to crown restorations of interest with a brush and the like. The restorations applied with the paste are air-sintered in an optimized sintering schedule by using a porcelain furnace for a dental technology. By sintering, coloring components, which are contained in the porcelain stains, fuse with the crown restorations.
Generally, porcelain stains are properly used for metal ceramic crown restorations and all ceramic crown restorations and, they are called as an internal stain or an external stain depending on parts to be applied.
The reason why properly using as described above is because since metal ceramic crown restorations and all ceramic crown restorations as basements have significantly different linear thermal expansion coefficients from each other, it is needed to use a porcelain stain having a linear thermal expansion coefficient matching with each of crown restorations in order to prevent the porcelain stain from peeling from applied surfaces, cracking, breaking and the like due to an exceeding stress caused by a difference in linear thermal expansion coefficients between the basement and the porcelain stain. Further, it is also the reason that situations for generating stresses are different between inner regions and surface regions of restorations.
Japanese patent No. 4006230 discloses a stain powder and a glazing powder for coloring or glazing full ceramic crowns, but these powders are limited to be used in diopside glass ceramics having a linear thermal expansion coefficient of 4−6×10−6 K−1.
Japanese Patent No. 2847084 discloses a low-temperature sintering stain material (porcelain stain) which contains phosphate glass as a main component, but its composition is limited as 30-80% by weight of P2O3 and 1-20% by weight of Al2O3.
[Patent Document 1] Japanese Patent No. 4006230
[Patent Document 2] Japanese Patent No. 2847084